Cycles particle hair UVs in compositor?

I am trying to figure out how to get access to the UVs of particle hair in the compositor, so that I can re-map textures to particle hair in post. However, I do not see how I go about making UVs for particle hair at all. I know I can plug in the UV texture coordinate in a material used on the hair, but I do not understand where it gets the UV data from, or how to have it show up in the renderlayer UV pass in the compositor.

there is a hair ifo node.